Different types of Sub Floors

Sub floors can be divided into three categories:

1) Concrete or screed,
2) Wooden (floorboards, plywood or chipboard)
3) Floor joists or battens.

Remember the finished floor will only be as good as the sub floor, so whichever sub floor you have, it is well worth the time and effort to get it right, or even consider installing a new one.

Concrete or screed

Concrete or screed sub floors must be both level and dry. They must be level to within plus or minus 3mm over a span of two metres.

You will also need to check the moisture content of the sub floor, which should be less than 4%. (max 65% relative humidity) You can do this with a moisture meter.   To properly test you should measure the amount of moisture the floor is giving off over a period. A simple surface test will only tell you what is going on the surface of the screed and not if the screed has dried out to any depth.

Regardless of what the moisture content is, you should use a barrier to prevent moisture affecting the wood flooring. Our concrete Primer is highly recommended. We use it on all glue down floors regardless even if the moisture level is showing low, as it is a primer and because although the moisture is low now it may not be at a different time of year. If it is a brand new concrete floor, it is advisable to leave it for at least 28 days before installing your solid wood flooring.

Wooden: Floorboards, Ply or chip board

A sub floor of floorboards or plywood is perfect for installing solid wood flooring; however, Hardwood flooring should not be used over chipboard because it may not be strong enough to hold the flooring.  Therefore it is advisable to lay 12 plywood first. Check for any squeaking and secure any loose boards, any rotten floorboards must be replaced. If the floorboards are not in good condition you could lay 12mm plywood first.

Wooden sub floors must also be level to within plus or minus 3mm over a two metre span.

The sub floor moisture content should be within 4% of your hardwood flooring to avoid over expansion or contraction. You could use a polyfoam underlay for soundproofing.

Floor Joists or Battens

As with any sub floor, joists or battens must be level to within plus or minus 3mm over a two metre span. The distances between the joists or battens will determine how many fixings are used.

Solid wood floors should be fixed every 250mm to 300mm. Engineered wood floors can be fixed every 400mm. Most houses in the UK have joists that are 400mm apart.  If you are fixing your hardwood floor to battens on top of a concrete sub floor, the concrete must comply with the conditions above.